Albert Barnes Commentary Exodus 4:26

"So he let him alone. Then she said, A bridegroom of blood [art thou], because of the circumcision." — Exodus 4:26 (ASV)

So he let him go—that is, God withdrew His visitation from Moses.

Moses sent Zipporah and her children back to Jethro before he went to Egypt (Exodus 18:2). The journey would have been delayed had he waited for the healing of the child.